The present invention broadly relates to zinc electroplating additive compositions and processes, and more particularly, to a stable aqueous concentrate containing hydrophobic brightening agents adapted for dilution with water for the make-up and replenishment of acid zinc or zinc alloy electroplating baths of the chloride and mixed chloride types.
It is conventional commercial practice to employ liquid concentrates of additive agents adapted for the make-up and replenishment of electroplating baths. Such additive agents are preferably provided in the form of an aqueous solution which can subsequently be diluted with water to form an electroplating bath containing the essential constituents within a preferred range. Similarly, a replenishment of the essential bath constituents is preferably performed employing such aqueous concentrates which are periodically and/or continuously added to the bath through liquid metering pumps as a function of the ampere-hour usage of the bath as being indicative of the consumption of certain of such ingredients. Acid zinc or zinc alloy electroplating baths of the types presently in widespread commercial use, employ various organic brightening agents to enhance the brightness, leveling and ductility of the zinc or zinc alloy deposit. Many of such organic primary brightening agents because of their hydrophobic nature are not readily soluble in water necessitating the use of organic solvents, organic hydrotropes and/or organic dispersing agents to prepare liquid concentrates of such additives for make-up and replenishment of acid zinc or zinc alloy electrolytes. The necessity of employing relatively large quantities of such supplemental solvents and dispersing agents substantially increases the cost of such concentrates and also imposes shipping restrictions due to the presence of solvents which are of a flammable nature. The presence of such supplemental organic dispersing agents in the liquid concentrates also constitutes a source of contamination of the electroplating bath frequently resulting in an undesirable lowering of the bath cloud point. In spite of the use of such supplemental organic agents in such concentrates for solubilizing the hydrophobic organic brightening agents, undesirable precipitates are formed when such concentrates are exposed to relatively low ambient temperatures such as encountered during shipment and storage in northern climates during the winter months. Under such conditions, precipitates are formed at relatively moderate temperatures which have been found cannot be redissolved when the concentrate is reheated to room temperature. The foregoing problem requires special shipping and storage conditions to prevent a "freezing out" of the hydrophobic organic brightener additives in such concentrates and in some instances, necessitates a discarding of such concentrate when appreciable quantities of insoluble precipitate have formed.
The present invention overcomes many of the problems and disadvantages associated with aqueous concentrates of the types heretofore known which completely or substantially completely eliminates the use of expensive flammable solvents, which substantially increases the stability of such concentrates even when subjected to relatively cool temperatures, which facilitates a dissolution of any precipitates formed by simply reheating the concentrate in the presence of agitation, and which does not introduce detrimental contaminants into the zinc electroplating bath.